Polymerization of dienes has generally been performed using various catalyst systems including rare-earth metals and nickel-based catalyst systems. For example, the catalysts for the cis-1,4 polymerization of butadiene are Ziegler-Natta (ZN)-type multi-component systems comprised of a rare-earth metal (e.g., Nd) carboxylate, ethyl-aluminum chloride, isobutyl aluminum hydride. Cis-1,4-polybutadiene has been produced by polymerization of 1,3-butadiene using a ZN catalyst system containing Ni(OOC8H15)2, and Al(C2H5)3 and the Lewis acids BF3O(C2H5)2 or TiCl4.
Transition metal-containing (e.g., nickel-based) catalyst systems generally produce polybutadiene with a cis content between 92-97%. The vast majority of the transition metal-containing catalyst systems use no ligands, and use what is referred to as “naked” transition metal such as “naked” nickel. PNP compounds have been used in lanthanide and early transition metal based systems, but have not seen usage in late transition metal (i.e. nickel) catalyst systems for the polymerization of butadiene.